This invention relates to wood treatment and, more particularly, to a conveying device which facilitates pressure treating of wood, and a related method.
Conventional wood preserving apparatuses have included a horizontally-oriented, cylindrical, pressurized treatment chamber or "autoclave," into which "charges" of lumber are placed. The lumber is moved on trams that run on small gauge railroad-like tracks. Various preserving chemicals flood the autoclave and the pressure therein is alternately lowered and increased to treat the lumber.
More particularly, a tram of untreated lumber is placed through one open door of the autoclave, another tram of untreated lumber is placed through the opposing open door at the other end of the autoclave, the doors are sealed and the wood is treated. The doors are then opened and each tram is pulled out the same end from which it was put in. The treating chemicals are allowed to drip off the treated lumber, the treated lumber is removed from the respective trams by, e.g., cranes, and new untreated lumber is placed on each tram, whereupon the process is repeated.
This method has at least two major disadvantages:
1) Having to load untreated and treated lumber on a tram at both ends of the autoclave precludes a smooth flow of lumber through the plant, and requires significant lumber handling; PA0 2) Because the treating solution is a government regulated hazardous material, any surface over which the lumber passes in the first forty eight hours after treatment must have primary and secondary containment with monitoring of leakage. Such a "drip pad" area (usually about 100 feet by 300 feet) is many times more expensive than a standard floor slab. PA0 1) If the rollers are driven by hydraulic motors inside the autoclave, cross contamination between hydraulic motor oil and treating liquid is inevitable and undesirable. PA0 2) The drive shaft pressure seals of the rollers which enter the autoclave are damaged by the repeated autoclave pressure treatment. PA0 3) Fitting the conveyor rollers inside the autoclave requires an increased internal diameter of a traditional autoclave. This results in a higher capital cost, plus the creation of much more wasted space in the autoclave, which must be filled with treatment fluid. PA0 1) Creating a one direction flow that requires less lumber handling; PA0 2) Eliminating maintenance problems, such as pressure seals, etc., which are characteristic of a conveyor system; and PA0 3) Lowering capital costs, through the use of a more compact operating area, eliminating the need for about 50 percent of the "drip" area required by the traditional two end load/removal method, eliminating the need for an enlarged treatment chamber necessitated by powered rollers, and allowing for lesser winch requirements.
Several attempts have been made to provide a smoother flow of lumber using a double door plant. For example, one apparatus replaces the trams and track with a powered roller conveyor which moves in only one direction from a non-hazardous material area, through the autoclave, and on to a drip pad area that is smaller than the conventional drip pad.
More particularly, this method includes driven spaced transverse rollers that rotate and advance the charges of lumber through the autoclave in one direction, i.e., in one end and out the other. The method is an improvement over the above-described tram and track version, but the following disadvantages are still associated with this alternate method:
Although the prior art described above eliminates some of the problems inherent in the wood treatment art, this prior art still does not disclose or teach the most cost efficient apparatus or the most time-efficient method for treating wood.